The present invention relates generally to starters, and more particularly to a starter system and a method for starting an internal combustion engine.
Conventional starters are normally designed as series-wound DC motors. Therefore, it is usual to choose a series-wound motor, as this type of motor supplies a relatively high starting torque to make the internal combustion engine xe2x80x9cturn overxe2x80x9d. However, this means that considerable currents flow at the high torques to be applied.
During a cold start, the internal combustion engine generates considerable torque in opposition to the starter motor, via the very high shearing forces in the engine oil, so that the starting current at low temperatures rises steeply and may be, for example, some hundreds of amperes in starter motors capable of driving large internal combustion engines. At the same time, the internal resistance of the starter battery rises as the temperature falls, severely limiting the available power or the discharge current that may be drawn. As a result of both these factorsxe2x80x94their effect increasing as the temperature fallsxe2x80x94it is not unusual for the starter battery to fail during a cold start, because the discharge current xe2x80x9cdemandedxe2x80x9d by the starter motor is too high.
Current technology offers a number of known proposals designed to make starting certain at low temperatures. Many of these proposals work by providing an additional short-term energy boost in the form of a storage capacitor, which is charged up slowly before the starting process. In some of these proposals, the battery and the pre-charged capacitor are connected in parallel for starting, so that both energy sources contribute to the start-up process (JP 02175350A (Isuzu) and JP 02175351A (Isuzu)). In other proposals, the storage capacitor for the starting process is separate from the starter battery, starting thus being achieved entirely via the energy stored in it (DE 41 35 025 A1 (Magneti Marelli) and U.S. Pat. No. 5,051,776 (Isuzu)). In other proposals of this nature, the starting energy required is provided via the potential difference across the starter battery (12V or 24V) by means of a DC-DC converter (a so-called up-converter), which first raises the voltage and then stores it in a capacitor (SU 1265388 A1 (Mosc Automech) and EP 0 390 398 A1 (Isuzu)). The higher voltage during starting, combined with a lower discharge current, thus allows the latter proposals to provide guaranteed starting even at low temperatures.
EP 0 403 051 A1 (Isuzu) also gives details of a process for charging a storage capacitor up to a certain variable voltage level only, dependent on the temperature of the engine coolant at the time, for the purpose of providing starting energy.
There is also a range of proposals for sensing the temperatures in the vehicle and influencing the control of electrical processes:
Thus, for example, EP 0 553 037 B1 (Magneti Marelli) gives details of a storage capacitor for feeding an electrical catalytic heating system, in which the capacitor discharge, and thus the degree of heating, is controlled as a function of the temperature.
There has been a further proposal to measure the vehicle battery temperature and vary the charging current, employing a change in generator excitation, as a function of the temperature; and of course the charging current at lower temperatures may thus be raised. This can obviously be employed, even at low temperatures, if the battery is xe2x80x9cresistant to chargingxe2x80x9d, to avoid increasing the charging time (DE 34 23 767 A1 (Bosch) and EP 0 621 990 B1 (Bosch)).
To avoid adversely affecting the function of other electrical consumers such as the ignition and fuel injection systemsxe2x80x94despite the steep fall in supply voltage during a cold start, the use of up-converters to maintain the supply voltage constant has also been recommended (EP 0 391 065 A2 (Bosch)).
Finally, WO 97/08456 (Clouth et al.) provides details of a modern high performance starter based on an alternator, where the starter battery DC voltage is converted and, in connection with this conversion, stepped up to a higher voltage level via an intermediate DC circuit. Special measures to guarantee a sure start at low temperatures are not specifically mentioned in this.
U.S. Pat. No. 5,325,042 gives details of a starter system for a combustion engine in the form of a turbine, with an electric starter, a starter battery, a power electronics module in the form of a voltage source converter, which actively varies the value of the discharge current drawn by the starter battery for the purpose of starting, and a control device based on pulse width modulation, feeding the power electronics module with the charging current to be varied.
DE 43 41 826 A1 gives details of an internal combustion engine with automatic shutdown, employing a sensor to detect the temperature of a starter battery and feed a control device. Depending on the measured temperature value, a decision is made on whether to shut the engine down when stopped at traffic lights or not.
IBM Technical Disclosure Bulletin Volume 37, No. 6A, June 1994, S. 609-610 mentions a battery charging and discharging circuit for portable equipment, in which the battery temperature is sampled and, depending on the result, the on-off ratio of the discharge current under load, and thus its mean value, may be varied. At low battery temperatures, this value is greater than at high temperatures.
Some of the proposals mentioned during this introduction, e.g. that from Mosc Automech, can avoid the battery failing when starting under cold conditions is wanted.
The invention provides a starter system for an internal combustion engine. It comprises an electric starter, a starter battery for warming up or starting the combustion engine, a temperature measuring device for measuring the temperature of the starter battery, a power electronics module, which actively varies the magnitude of a discharge current drawn from the starter battery for the purpose of warming up or starting the engine, and a control device. The control device feeds the power electronics module with the value of the discharge current to be varied, where, at low battery temperatures, the maximum discharge current is lower than at high temperatures.
According to another aspect, the invention provides a method for starting an internal combustion engine with an electric starter, a starter battery and a device for measuring the temperature of the starter battery. The method comprises measuring the starter battery temperature, determining the maximum discharge current as a function of the measured battery temperature, and actively limiting the discharge current drawn by the electric starter for the purpose of starting or warming-up to the calculated maximum value.
Other features are inherent in the disclosed system, computer program product and method or will become apparent to those skilled in the art from the following detailed description of embodiments and its accompanying drawings.